Shallow water environments are typically variable. For example, acoustic signals can be refracted (or reflected) from various boundaries including the sea surface and the sea bottom. Acoustic signals can also be refracted (reflected) within the water column itself, such as from temperature fronts and internal waves. Internal waves, for example, can produce large fluctuations on shallow water signals, both in amplitude and phase. These fluctuations may affect underwater array processing results, such as for source localization and inverse problem (medium) studies.
In general, internal waves are gravity waves that may oscillate within a fluid medium. (Nonlinear solitary internal waves are typically referred to as solitons). For example, an internal wave may propagate along the boundary between low and high density water regions. Internal waves may propagate vertically as well as horizontally.
It is desirable to detect fluctuations, such as internal waves, in the water column.